A lightweight and portable approach to making concurrent failures reproducible

Abstract. Concurrent programs often exhibit bugs due to unintended interferences among the concurrent threads. Such bugs are often hard to reproduce because they typically happen under very specific interleaving of the executing threads. Basically, it is very hard to fix a bug (or software failure) in concurrent programs without being able to reproduce it. In this paper, we present an approach, called ConCrash, that automatically and deterministically reproduces concurrent failures by recording logical thread schedule and generating unit tests. For a given bug (failure), ConCrash records the logical thread scheduling order and preserves object states in memory at runtime. Then, ConCrash reproduces the failure offline by simply using the saved information without the need for JVM-level or OS-level support. To reduce the runtime performance overhead, ConCrash employs a static data race detection technique to report potential possible race conditions, and only instruments such places. We implement the ConCrash approach in a prototype tool for Java and experimented on a number of multi-threaded Java benchmarks. As a result, we successfully reproduced a number of real concurrent bugs (e.g., deadlocks, data races and atomicity violation) within an acceptable overhead.

Dependent types for program understanding

Abstract. Weakly-typed languages such as Cobol often force programmers to represent distinct data abstractions using the same low-level physical type. In this paper, we describe a technique to recover implicitlydefined data abstractions from programs using type inference. We present a novel system of dependent types which we call guarded types, a pathsensitive algorithm for inferring guarded types for Cobol programs, and a semantic characterization of correct guarded typings. The results of our inference technique can be used to enhance program understanding for legacy applications, and to enable a number of type-based program transformations.